Photolithographic method for forming a coating layer

ABSTRACT

A method for forming a coating layer includes spraying coating material having a first flowability onto a substrate; performing a first spin coating process with a first spin speed to form an initial coating layer; and performing a first baking process to the initial coating layer to form a first material layer having a second flowability and a second material layer having a third flowability. The third flowability is less than the first flowability but larger than the second flowability, which is less than the first flowability. Further, the method includes performing a second spin coating process with a second spin speed to drive the coating material in the second material layer flowing on the surface of the first material layer to form a third material layer with a uniform thickness, and performing a second baking process to form a final coating layer on the substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of Chinese patent application no.CN201410114618.0, filed on Mar. 25, 2014, the entire content of which isincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of semiconductormanufacturing technology and, more particularly, relates a coating layerformation method in a photolithographic process.

BACKGROUND

In semiconductor manufacturing, functional integrated circuits can befabricated on a semiconductor substrate by using a series of processessuch as photolithography, etching, doping, deposition, planarizing, andcleaning. Among these processes, the photolithography process isespecially important, because it may define areas for performing theetching and/or doping processes.

During the photolithography process, a photoresist layer is formed on asemiconductor substrate by a spin-on-coating technique and fixed orcompletely cured by a baking process first. Then, the formed photoresistlayer may be put in a photolithography machine. Next, the photoresistlayer may be exposed, transferring patterns in a mask into the exposedphotoresist layer. Finally, the exposed photoresist layer may be bakedand developed, forming patterns in the photoresist layer.

However, as the photoresist layer becomes thicker, the uniformity of thethickness may decrease significantly. Thus, the subsequent exposureprocess and other processes may be impacted. For example, the line widthmay change during the exposure process. Thus, the semiconductormanufacturing yields may decrease. Similarly, when forming other coatinglayers (e.g., polyimide) on the semiconductor substrate using thespin-on-coating technique, as the thickness of the coating layerincreases, the thickness uniformity may decrease. The disclosed methodsare directed to solve one or more problems set forth above and otherproblems.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure provides a photolithographic methodfor forming a coating layer. The method includes spraying coatingmaterial having a first flowability to a top surface of a providedsemiconductor substrate, and performing a first spin coating process byrotating the semiconductor substrate with a first spin speed to form aninitial coating layer covering the top surface of the semiconductorsubstrate. The method also includes performing a first baking process tothe initial coating layer to form a first material layer having a secondflowability and a second material layer having a third flowability. Thesecond flowability is less than the first flowability and the thirdflowability is larger than the second flowability but less than thefirst flowability. Further, the method includes performing a second spincoating process by rotating the semiconductor substrate with a secondspin speed to drive the coating material in the second material layerflowing on the surface of the first material layer to form a thirdmaterial layer with a uniform thickness, and performing a second bakingprocess to the first material layer and the third material layer to forma final coating layer on the top surface of the semiconductor substrate.

Another aspect of the present disclosure provides a photolithographicmethod for forming a coating layer. The method includes spraying coatingmaterial having a first flowability to a top surface of a providedsemiconductor substrate, performing a first spin coating process with afirst spin speed and performing a first baking process simultaneously toform a first material layer having a second flowability and a secondlayer having a third flowability, performing a second spin coating witha second spin speed to drive the coating material in the second materiallayer flowing on the surface of the first material layer to form a thirdmaterial layer with a uniform thickness, and performing a second bakingprocess to the first material layer and the third material layer to forma final coating layer on the top surface of the semiconductor substrate.

Other aspects of the present disclosure can be understood by thoseskilled in the art in light of the description, the claims, and thedrawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present disclosure.

FIG. 1 illustrates a flow chart of an exemplary photoresist layerformation method;

FIGS. 2-6 illustrate sectional views of a semiconductor structurecorresponding to certain states of an exemplary photolithographic methodfor forming a coating layer consistent with the disclosed embodiments;

FIG. 7 illustrates a top view of an exemplary semiconductor substratewith certain testing points located on surface consistent with thedisclosed embodiments;

FIGS. 8-14 illustrate sectional views of a semiconductor structurecorresponding to certain states of another exemplary photolithographicmethod for forming a coating layer consistent with the disclosedembodiments;

FIGS. 15-17 illustrate sectional views of a semiconductor structurecorresponding to certain states of another exemplary photolithographicmethod for forming a coating layer consistent with the disclosedembodiments; and

FIG. 18 illustrates a flow chart of an exemplary photolithographicmethod for forming a coating layer consistent with the disclosedembodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of theinvention, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts. It is apparent that thedescribed embodiments are some but not all of the embodiments of thepresent invention. Based on the disclosed embodiments, persons ofordinary skill in the art may derive other embodiments consistent withthe present disclosure, all of which are within the scope of the presentinvention.

As illustrated in the background section, as the thickness of the to beformed photoresist layer or other coating layers increases, thethickness uniformity of the formed photoresist layer or other coatinglayers may decrease. Thus, the production yields may be impacted.

FIG. 1 illustrates a flow chart of an exemplary photoresist layerformation method. As shown in FIG. 1, the process for forming aphotoresist layer may include the following steps:

Step S101, placing a semiconductor substrate on a wafer chunk of a spincoating machine, holding the semiconductor substrate by vacuum.

Step S102, spraying photoresist to the top surface of the semiconductorsubstrate. More specifically, a nozzle filled with the photoresist maybe moved to above the semiconductor substrate, and may spray thephotoresist to the top surface of the semiconductor substrate. Thesemiconductor substrate may be in a stationary status.

Step S103, spin coating and driving the photoresist to cover the wholetop surface of the semiconductor substrate. More specifically, the waferchunk may be rotated by a motor. Thus, the semiconductor substrate fixedon the wafer chunk may rotate together. Photoresist may spread to theedge region of the semiconductor substrate because of a centrifugalforce and may cover the whole top surface of the semiconductorsubstrate.

Step S104, baking the semiconductor substrate to evaporate the solventin the photoresist, forming a photoresist layer covering the top surfaceof the semiconductor substrate.

However, under the impact of the centrifugal force generated by therotation of the semiconductor substrate, the photoresist may aggregatemore in the edge region while aggregate less in the central region ofthe semiconductor substrate. Thus, the surface of the finally formedphotoresist layer may have a concaved shape. That is, the thickness ofthe photoresist layer formed in the edge region of the semiconductorsubstrate may be larger than the thickness of the photoresist layerformed in the central region of the semiconductor substrate.

Further, to form a thicker photoresist layer, more photoresist may besprayed on the semiconductor substrate. As more photoresist is spayed onthe semiconductor substrate, during the subsequent spin coating process,the quantity of the photoresist aggregating at the edge region of thesemiconductor substrate may be significantly different from the quantityof the photoresist aggregating at the central region of thesemiconductor substrate because of an increased centrifugal force. Thus,the finally formed photoresist layer may have an obvious variation inthickness. More specifically, the thickness of the photoresist layerformed in the edge region may be significantly larger than the thicknessof the photoresist layer formed in the central region. As thephotoresist layer thickness uniformity decreases, the production yieldsmay decrease.

Thus, this disclosure provides an improved photoresist layer formationmethod. In this method, the photoresist layer may be formed by a doublecoating method. The formed photoresist layer may be relatively thick,but the thickness of the formed photoresist layer may be more uniform.The double coating method for forming a photoresist layer may includespraying a first photoresist material on the top surface of thesemiconductor substrate; performing a first spin coating and driving thefirst photoresist material to cover the whole top surface of thesemiconductor substrate; and baking the first photoresist material andforming a first photoresist layer.

The double coating method for forming a photoresist layer may furtherinclude spraying a second photoresist material on the surface of thefirst photoresist layer; performing a second spin coating process anddriving the second photoresist material to cover the whole surface ofthe first photoresist layer, and baking the second photoresist materialand forming a second photoresist layer. The first photoresist layer andthe second photoresist layer together form the final photoresist layer.The thickness of the final photoresist layer is the sum of the thicknessof the first photoresist layer and the second photoresist layer.

The photoresist layer formed by the double coating method may berelatively thick, and may have an improved thickness uniformity.However, during the spin coating process, certain amount of photoresistmay be thrown out of the semiconductor substrate surface. Because thephotoresist material is sprayed twice (the first photoresist materialand the second photoresist material) to the semiconductor substrate,during the spin coating process, more photoresist may be thrown out ofthe semiconductor substrate. Thus, the photoresist layer formationprocess may consume a large amount of photoresist, resulting in aproduction cost increase and generating more wastage. Further, becausemore photoresist is thrown out of the semiconductor substrate, themanufacturing equipment may get contaminated more easily.

Thus, according to the disclosed embodiments, after spraying the coatingmaterial on the top surface of the semiconductor substrate, a first spincoating process is performed to drive the coating material covering thewhole top surface of the semiconductor substrate. Then, a first bakingprocess is performed to the semiconductor substrate, forming a firstmaterial layer and a second material layer. Next, a second spin coatingprocess is performed, driving the coating material in the secondmaterial layer to flow on the surface of the first material layer, untila uniformly-thicknessed third material layer is formed. After the secondspin coating process, a second baking process is performed to thesemiconductor substrate, forming a coating layer on the top surface ofthe semiconductor substrate.

Thus, in the disclosed photolithographic method for forming a coatinglayer, by performing the first baking process, the coating material mayform the cured first material layer and the flowable second materiallayer. The first material layer may have a uniform thickness. Further,by performing the second spin coating process, the coating material inthe second material layer may be redistributed and may form theuniformly-thicknessed third material layer. Thus, after performing thesecond baking process, the uniform thickness coating layer may beformed. In addition, when applying this method to fabricate certainrelatively thick coating layers, the formed coating layer may be uniformin thickness. Thus, semiconductor manufacturing yields may be enhanced.

FIG. 18 illustrates a flow chart of an exemplary photolithographicmethod for forming a coating layer consistent with the disclosedembodiments. FIGS. 2-6 illustrate sectional views of a semiconductorstructure corresponding to certain states of an exemplary coating layerformation method consistent with the disclosed embodiments.

As shown in FIG. 18, at the beginning of the coating layer formationprocess, a semiconductor substrate is provided and is hold on a waferchunk of a spin coating machine (S201). Then coating material is sprayedto the top surface of the semiconductor substrate (S202). FIG. 2illustrates sectional views of a semiconductor structure correspondingto certain states of an exemplary coating layer formation methodconsistent with the disclosed embodiments.

As shown in FIG. 2, a semiconductor substrate 200 is provided, andcoating material 201 is sprayed to the top surface of the semiconductorsubstrate 200. More specifically, the semiconductor substrate 200 may bea bare wafer, or may be a substrate having certain semiconductorstructures or devices. The semiconductor substrate 200 may be made ofsilicon, germanium, silicon germanium, silicon on insulator, germaniumon insulator, glass, or other materials. The top surface of thesemiconductor substrate 200 may need to be coated with the coatingmaterial 201 to form a coating layer. The semiconductor substrateincludes a central region (center area of the semiconductor substrate)and an edge region (edge area of the semiconductor substrate).

In one embodiment, the coating material 201 may be a photoresist. Thus,a photolithography process may be performed on the substrate 200subsequently. In certain other embodiments, the coating material 201 maybe other materials that compatible with the spin coating process. Forexample, the coating material 201 may be polyimide. Further, the coatingmaterial 201 may contain certain amount of solvent making the coatingmaterial 201 having a first flowability. Thus, during the subsequentspin coating process, the coating material 201 may flow on the topsurface of the semiconductor substrate 200, and may cover the topsurface of the substrate 200.

More specifically, the semiconductor substrate 200 may be placed on thewafer chunk of a spin coating machine. The wafer chunk may have certainvacuum structures (e.g., vacuum holes and/or vacuum trenches). Thesemiconductor substrate 200 may be held steady by these vacuumstructures.

Next, the coating material 201 may be sprayed onto the top surface ofthe semiconductor substrate 200. The coating material 201 may be aphotoresist. More specifically, a nozzle filled with the photoresistmaterial may be moved to above or close to the central region of thesemiconductor substrate 200. The nozzle may keep certain distance fromthe top surface of the semiconductor substrate 200. The semiconductorsubstrate 200 may be in a stationary status. Then the coating material201 may be sprayed onto the top surface of the semiconductor substrate200 in or close to the central region.

In one embodiment, the coating material 201 is located in the centralregion on the top surface of the semiconductor substrate 200. Thequantity of the sprayed coating material 201 may be determined by thethickness of the photoresist layer to be formed. The detailed type ofphotoresist may be determined by photolithography process parameters(e.g., line width), and by the etching process parameters.

Moreover, prior to spraying the coating material 201, certain surfactant(or primer) may be sprayed to the top surface of the semiconductorsubstrate. The surfactant may reduce the flow resistance on the topsurface of the semiconductor substrate, thus the photoresist may flowmore easily during the subsequent spin coating process. Thereby, theamount of the consumed photoresist may be reduced, and the cost may bereduced accordingly.

More specifically, a nozzle filled with the surfactant material may bemoved to above the top surface of the semiconductor substrate 200. Thenozzle may keep certain distance from the top surface of thesemiconductor substrate 200. The semiconductor substrate 200 may be in astationary status. Then the surfactant material may be sprayed to thetop surface of the semiconductor substrate 200 located in or close tothe central region. Next, the semiconductor substrate 200 may be rotatedtogether with the wafer chunk. Under a centrifugal force, the surfactantmaterial may spread to the edge region along the top surface of thesemiconductor substrate 200. Finally, the surfactant material may coverthe entire top surface of the semiconductor substrate 200. The excessivesurfactant material is thrown out of the semiconductor substrate 200during the spin process.

Returning to FIG. 18, a first spin coating process is performed to forman initial coating layer (S203). FIG. 3 illustrates sectional views of asemiconductor structure corresponding to certain states of an exemplarycoating layer formation method consistent with the disclosedembodiments.

As shown in FIG. 3, an initial coating layer 202 coving the whole topsurface of the semiconductor substrate may be formed after perform thefirst spin coating process.

More specifically, during the first spin coating process, thesemiconductor substrate may be rotated with a first spin speed. Thecoating material 201 (FIG. 2) may cover the entire top surface of thesemiconductor substrate 200 and may form an initial coating layer 202.

By rotating the semiconductor substrate 200, the centrifugal force maydrive the coating material 201 flowing toward the edge region of thesemiconductor substrate 200. The coating material 201 may spread on thetop surface of the semiconductor substrate 200, and may form the initialcoating layer 202 on the top surface of the semiconductor substrate 200.During rotating the semiconductor substrate 200, gas may be blown to thebackside of the semiconductor substrate 200 (a surface of thesemiconductor substrate 200 without forming the initial coating layer202). More specifically, the gas may be blown close to the edge regionon the backside of the semiconductor substrate 200. The blown gas mayprevent the coating material 201 from flowing toward the backside of thesemiconductor substrate 200. The gas may be nitrogen or other inertgases.

In certain embodiments, the gas may be blown in a directionperpendicular to the backside of the semiconductor substrate 200. Afterthe gas hitting the backside, the gas may flow toward the edge along theback surface of the semiconductor substrate 200. The formed gas flow mayprevent the coating material 201 from flowing to the backside of thesemiconductor substrate 200 during the first spin coating process. Thus,the photoresist contamination to the back surface of the semiconductorsubstrate 200 may be reduced or eliminated. In other embodiments, thedirection of the blown gas may be inclined to the back surface of thesemiconductor substrate 200.

Further, the first spin speed used for performing the first spin coatingprocess may be a relatively slow speed. During the spin coating process,the amount of the coating material 201 flowed to the edge region of thesemiconductor substrate 200 may be proportional to the centrifugalforce. Thus, when the first spin speed is slow, the amount of thecoating material 201 flowed to the edge region of the semiconductorsubstrate 200 may be less because of the smaller centrifugal force.Thereby, the formed initial coating layer 202 may be thicker in thecentral region and thinner in the edge region. During a subsequentsecond spin coating process, the flowable initial coating layer 202 withcertain thickness may flow to the edge region and may finally form auniformly-thicknessed coating layer.

Further, certain amount of the coating material 201 may be thrown out ofthe semiconductor substrate 200 during the first spin coating process.If the first spin coating speed is too fast, a large amount of thecoating material 201 may be thrown out of the semiconductor substrate.Thus, the amount of the coating material 201 left on the top surface ofthe semiconductor substrate 200 may be not enough for forming thedesired thicknessed coating layer. Thereby, the first spin coatingprocess may use a relative low speed. After the first spin coatingprocess, there may be enough coating material 201 left on the topsurface of the semiconductor substrate 200, and is good for forming thedesired thicknessed coating layer.

Further, if the first spin speed used in the first spin coating processis too fast, the formed initial coating layer 202 may be thicker in theedge region and thinner in the central region. During the subsequentsecond spin coating process, because the impact from the centrifugalforce, the certain thicknessed flowable initial coating layer 202 may behard to flow back to the central region. Thus, the relatively thinnedcentral region in the initial coating layer 202 may not be filled andmay have defects. The finally formed coating layer may still have theproblem of being thicker in the edge region and thinner in the centralregion.

According to the above analysis, the first spin speed may range from 400rpm (revolutions per minute) to 1000 rpm. In other embodiments, thefirst spin speed may be determined based on the viscosity of the coatingmaterial used in the actual process.

Returning to FIG. 18, a first baking process is performed to form afirst material layer and a second material layer (S204). FIG. 4illustrates sectional views of a semiconductor structure correspondingto certain states of an exemplary coating layer formation methodconsistent with the disclosed embodiments.

As shown in FIG. 4, after the first spin coating process, a first bakingprocess may be performed to the coating material layer 201 (FIG. 2) (orthe initial coating layer 202 shown in FIG. 3), forming a first materiallayer 203 and a second material layer 204 on the top surface of thesemiconductor substrate successively. The first material layer 203 mayhave a second flowability. The second material layer 204 may have athird flowability. Further, the second flowability may be smaller thanthe first flowability, and the third flowability may be larger than thesecond flowability but less or equal to the first flowability.

More specifically, during the first baking process, solvent in the lowerportion of the initial coating layer 202 contacting with the top surfaceof the semiconductor substrate 200 may be evaporated. Thus, the lowerportion of the initial layer 202 may be cured and may form the firstmaterial layer 203. The cured first material layer 203 may have a secondflowability. And, the second flowability may be smaller than the firstflowability. The relatively smaller second flowability may keep thethickness of first material layer 203 constant during a subsequentsecond spin coating process. And the thickness of the upper portion ofthe initial coating layer 202 (FIG. 3) having a relatively largerflowability may be reduced during the subsequent second spin coatingprocess. That is, the mass of the initial coating layer 202 (FIG. 3)having a relatively larger flowability may be reduced.

During the second spin coating process, because the first material layer203 is cured, the thickness of the first material layer may keepunchanged. While, for the second material layer 204, because it maystill have a relatively larger flowability, during the subsequent secondspin coating process, coating material in the second material layer mayflow to the edge region of the semiconductor substrate 200.

Further, because the mass of the flowable initial coating layer 202 maybe reduced, the flowable initial coating layer 202 (e.g., the secondmaterial layer 204) may be impacted less by the centrifugal force. Thus,the large amount of the second material layer 204 flowing to the edgeregion may be avoided. The accumulation of the second material layer 204in the edge region may be prevented. Thereby, the sum of the thicknessof the first material layer 203 and the second material layer 204 may beequal in every region.

In addition, during the first backing process, the back surface (thesurface opposite to the top surface of the semiconductor substrate 200)of the semiconductor substrate may be heated uniformly. Thus, everyregion of the semiconductor substrate may obtain the same amount ofheat. Accordingly, the initial coating layer 202 may obtain the samequantity of heat in every region. The formed first material layer 203 bythe first backing process may have the same thickness in every region.That is, the first material layer 203 has a uniform thickness.

Moreover, if the first baking process lasts too long, or the firstbaking process uses a temperature that is too high, the formed curedfirst material layer 203 may be too thick. Thus, the formed secondmaterial layer 204 having the relatively larger flowability may be toothin, which may impact on forming a coating layer with a uniformthickness. In certain scenarios, the initial coating layer 202 may becured completely, and may substantially impact forming the uniformcoating layer.

On the other hand, if the first baking process lasts too short, or thefirst baking process uses a temperature that is too low, the formedcured first material layer 203 may be too thin. And the formed secondmaterial layer 204 having the relatively larger flowability may be toothick. After performing the second spin coating process, because thesecond material layer 204 is too thick, the previously formed coatinglayer in the edge region of the semiconductor substrate 200 may becomethicker.

Thus, according to the disclosed embodiments, the first baking processmay be a fast baking process, with a temperature ranging from 60° C. to200° C., and a baking duration ranging from 1 second to 300 seconds.

Returning to FIG. 18, a second spin coating process is performed to forma third material layer (S205). FIG. 5 illustrates sectional views of asemiconductor structure corresponding to certain states of an exemplarycoating layer formation method consistent with the disclosedembodiments.

As shown in FIG. 5, performing a second spin coating process to thesemiconductor substrate 200 using a second spin speed, wherein, thesecond material layer 204 (FIG. 4) having the third flowability may flowon the surface of the first material layer 203 and may form a thirdmaterial layer 205 with a uniform thickness.

More specifically, after performing the first baking process, the firstmaterial layer 203 on the top surface of the semiconductor substrate 200may be cured. Thus, during the second spin coating process, the firstmaterial layer 203 may not flow. However, the second material layer 204having the third flowability (larger than the second flowability butsmaller than the first flowability) may flow on the surface of the firstmaterial layer 203, and may form the third material layer 205.

Further, the second spin speed used to rotate the semiconductorsubstrate 200 during the second spin coating process may be faster thanthe first spin speed. Thus, the second material layer 204 located in thecentral region may flow to the edge region. The surface of the secondmaterial layer 204 may be planarized, forming the uniformly-thicknessedthird material layer 205.

After the first spin coating process, the second material layer 204 maybe thicker in the central region and thinner in the edge region. If thesecond spin speed is slower than the first spin speed, due to thereduced centrifugal force, the second material layer 204 may have areduced ability to move from the central region to the edge region.Thus, after the second spin coating process, the second material layer204 may be still thicker in the central region and thinner in the edgeregion, which may impact forming the uniformed thicknessed thirdmaterial layer 205.

According to the above analysis, the second spin speed may be fasterthan the first spin speed. The second spin speed may range from 1000 rpmto 2000 rpm. In other embodiments, the second spin speed may bedetermined by considering the viscosity of the coating material and theaptitude of the first spin speed.

Returning to FIG. 18, further, a second baking process is performed toform a coating layer on the top surface of the semiconductor substrate(S206). FIG. 6 illustrates sectional views of a semiconductor structurecorresponding to certain states of an exemplary coating layer formationmethod consistent with the disclosed embodiments.

As shown in FIG. 6, after the second spin coating process, a secondbaking process is performed to the first material layer 203 (FIG. 5) andthe third material layer 205 (FIG. 5), forming a coating layer 206 onthe top surface of the semiconductor substrate 200.

More specifically, during the second backing process, solvent in thefirst material layer 203 and in the third material layer 205 may befurther evaporated. Thus, the first material layer 203 and the thirdmaterial layer 205 may be solidified. The first material layer 203 andthe third material layer 205 may be transformed into the coating layer206. The coating layer 206 may have an improved adhesion to the topsurface of the semiconductor substrate 200.

In one embodiment, the second baking process may be performed with atemperature ranging from 90° C. to 400° C., and a baking durationranging from 30 seconds to 1000 seconds.

According to the above analysis, the first material layer 203 may have auniform thickness. After the second spin coating process, the thirdmaterial layer 205 formed on the surface of the first material layer 203may also have a uniform thickness. Thus, after evaporating the solventin the first material layer 203 and the third material layer 205 byperforming the second backing process, the uniformly-thicknessed coatinglayer 206 may be formed.

To test the performance of the coating layer formed by the disclosedmethod, photoresist layers formed by the single coating method, thedouble coating method, and the disclosed method respectively arefabricated and compared. The targeted thickness of the photoresist layerto be formed on the top surface of a semiconductor substrate is 100 μm.FIG. 7 illustrates a top view of the semiconductor substrate withcertain testing points on the surface. As shown in FIG. 7, the testingpoints include testing points 1-9.

Table 1 lists the photoresist layer thickness measured at these testingpoints locations corresponding respectively to photoresist layers formedby the single coating method, the double coating method, and thedisclosed method. Further, Table 1 also lists the average thickness andthe thickness variation calculated based on the measured thickness datacorresponding to the three photoresist layers respectively. At the end,Table 1 lists the photoresist mass consumed by the single coatingmethod, the double coating method, and the disclosed methodrespectively.

TABLE 1 Coating layer Coating layer Coating layer thickness thicknessthickness Testing (single coating (double coating (disclosed pointsmethod, μm) method, μm) method, μm) 1 95 104 97 2 101 98 102 3 107 101105 4 105 99 100 5 97 99 99 6 93 103 98 7 100 99 101 8 103 97 100 9 96104 98 Average 99.67 100.44 100.00 thickness (μm) Thickness 7.00 3.483.96 variation (%) Photoresist 8.5 13 8.5 usage (g)

As shown in Table 1, the photoresist layer formed by the disclosedmethod has a thickness variation 3.96%, and the photoresist layer formedby the single coating method has a thickness variation 7.00%. Thus, thethickness of the photoresist layer formed by the disclosed method ismore uniform. Further, the photoresist layer formed by the disclosedmethod consumes 8.5 grams photoresist, and the photoresist layer formedby the double coating method consumes 13 grams photoresist. Thus,embodiments consistent with the present disclosure may save cost. Thephotoresist layer formed by the disclosed method has relatively betteruniformity and consumes less photoresist, thus is an optimized option.

This disclosure proves another photolithographic method for forming acoating layer. More specificity, after the first spin coating processbut prior the second backing process, the first backing process may beperformed and repeated one or more times. Further, after each firstbacking process, a second spin coating process may be performed. That isthe first baking process and the second spin coating process may beperformed and repeated alternatively. Thus, prior performing the secondbaking process, a third material layer having a uniform thickness may beformed. Thereby, a uniformly-thicknessed coating layer may be formed.

FIGS. 8-14 illustrate sectional views of a semiconductor structurecorresponding to certain states of another exemplary photolithographicmethod for forming a coating layer consistent with the disclosedembodiments.

In one embodiment, after the first spin coating process but prior thesecond baking process, the first baking process may be repeated 3 times.In other embodiments, the first baking process may be repeated differenttimes.

As shown in FIG. 8, a semiconductor substrate 300 is provided, a secondmaterial layer 303 and a fourth material layer 304 are formed on the topsurface of the semiconductor substrate 300.

More specifically, a coating material (no shown) may be sprayed to thetop surface of the semiconductor substrate 300. The coating material mayhave a first flowability. Then, a first spin coating process may beperformed by using a first spin speed to rotate the semiconductorsubstrate 300. During the spin coating process, the coating material maycover the whole top surface of the semiconductor substrate, forming aninitial coating layer (not shown).

Next, the first baking process may be performed for a first time to bakethe coating material. Thus, the second material layer 303 and a fourthmaterial layer 304 may be formed successively on the top surface of thesemiconductor substrate. The second material layer 303 may have a secondflowability. Moreover, the second flowability may be smaller than thefirst flowability. The fourth material layer 304 may have a thirdflowability, and the third flowability may be larger than the secondflowability, but equal or less than the first flowability.

The material property and formation process of the semiconductorsubstrate 300, the coating material, the first spin coating process, thesecond material layer 303, the fourth material layer 304, and the firstbaking process are similar with the previous embodiment, wherein thesemiconductor substrate 200 (FIG. 2), the coating material 201 (FIG. 2),the first spin coating process, the first material layer, and the firstbaking process are illustrated, thus, are omitted here.

As shown in FIG. 9, further, a second spin coating process is performedfor the first time by rotating the semiconductor substrate 300 with asecond spin speed, driving the coating material in the fourth materiallayer 304 (FIG. 8) to flow toward the edge region. Thus, the fourthmaterial layer 304 may be transformed into a fifth material layer 305.

In this embodiment, the process requirements for performing the secondspin coating process for the first time may be lower than the processrequirements for performing the second spin coating in the previousembodiment. More specifically, after performing the second spin coatingfor the first time, the fifth material layer 305 may not be requiredstrictly to have a uniform thickness. The fifth material layer 305 maybe thicker in the central region and thinner in the edge region.

The second spin speed may be higher than the first spin coating speed.The second spin speed may range from 1000 rpm to 2000 rpm.

As shown in FIG. 10, the first baking of the semiconductor substrate 300is performed for a second time. After the baking process, the secondmaterial layer 303 (FIG. 9) may have an increased thickness and may betransformed into a sixth material layer 306. The fifth material layer305 (FIG. 9) may have a reduced thickness and may be transformed into aseventh material layer 307.

When the to-be-formed coating layer is significantly thick, afterperforming the second spin coating one time, it may still be difficultto form the uniformly-thicknessed third material layer. Thus, the firstbaking process may be performed for a second time. The cured secondmaterial layer 303 may have an increased thickness and may betransformed into the sixth material layer 306. While, the flowable fifthmaterial layer 305 may have a reduced thickness and may be transformedinto the seventh material layer 307. Thus, when perform the second spincoating process for a second time subsequently, an eighth material layerhaving a smaller thickness variation than the fifth material layer 305may be formed. The uniformly-thicknessed third material layer may beformed step by step.

When performing the first baking for the first time, the baking processmay be may be a fast baking process. The detailed process parameter ofthe first time first backing process may be determined by the actualprocess requirements.

As shown in FIG. 11, the second spin coating process is performed forthe second time to the semiconductor substrate 300 to transform theseventh material layer 307 (FIG. 10) into the eighth material layer 308.

After performing the second spin coating process for the second time,the eighth material layer 308 having a smaller thickness variation thanthe seventh material layer 307 may be formed. The formed eighth materiallayer 308 may have a reduced thickness variation in every region, and isgood for forming a uniformly-thicknessed coating layer. Further, thespin speed used in the second time spin coating process may be higherthan the spin speed used in the first time spin coating process.

As shown in FIG. 12, performing the first baking of the semiconductorsubstrate 300 for a third time. During the third time baking process,the sixth material layer 306 (FIG. 11) may have an increased thicknessand may be transformed into a first material layer 309. The eighthmaterial layer 308 (FIG. 11) may have a reduced thickness and may betransformed into a ninth material layer 310.

The function of the third time first baking process is similar with thesecond time first baking process as illustrated before, thus is omittedhere.

As shown in FIG. 13, the second spin coating process is performed forthe third time to the semiconductor substrate 300, transforming theninth material layer 310 (FIG. 12) into an uniformly-thicknessed thirdmaterial layer 311.

During the third time second spin coating process, coating material inthe ninth material layer 310 may be redistributed on the surface of thefirst material layer 309, and may be further planarized to form theuniform thicknessed third material layer 311. The spin speed for thethird time second spin coating process may be higher than the spin speedfor the second time second spin coating process.

As shown in FIG. 14, after the third time second spin coating process,the second baking process may be performed to bake the first materiallayer 309 (FIG. 13) and the third material layer 311 (FIG. 13). Thus, acoating layer 312 may be formed on the top surface of the semiconductorsubstrate 300.

The function and process parameters of the second baking process aresimilar with the second baking process in the previous embodimentillustrated before, thus are omitted here. The thickness of the formedcoating layer 312 may range from 50 μm to 5000 μm.

According to the above illustrations, after the first spin coatingprocess but prior to the second baking process, the first baking processmay be repeated three times. Moreover, after each first baking process,the second spin coating process may be performed. In other embodiments,after the first spin coating process but prior to the second bakingprocess, the first baking process may be repeated different times, suchas one, two, five, eight, etc. depending on the actual processrequirements.

In addition, after each first baking process, the second spin coatingprocess may be performed. For example, when a to-be-formed coating layeris too thick, performing the second spin coating once may be not able toform the uniformed thicknessed third material layer. Thus, the secondspin coating process may be performed multiple times, until theuniformed thicknessed third material layer is formed after the lastsecond spin coating process. The finally formed third material layer maybe thick and may have uniform thickness. Thus, the finally formedcoating layer may be thick and may have uniform thickness.

This disclosure provides another photolithographic method for forming acoating layer. In this method, the first spin coating process and thefirst baking process may be performed together to form the cured firstmaterial layer and the flowable second material layer. Next, the secondspin coating process may be performed, transforming the second materiallayer into the uniformly-thicknessed third material layer, and forming auniformly-thicknessed coating layer.

FIGS. 15-17 illustrate sectional views of a semiconductor structurecorresponding to certain states of an exemplary photolithographic methodfor forming a coating layer consistent with the disclosed embodiments.

As shown in FIG. 15, a semiconductor substrate 400 is provided, a firstmaterial layer 402 and a second material layer 403 are formedsuccessively on the top surface of the semiconductor substrate 400. Morespecifically, certain coating material (not shown) may be sprayed to thetop surface of the semiconductor substrate 400. The coating material mayhave a first flowability. Then the first spin coating process may beperformed by using a first spin speed to rotate the semiconductorsubstrate 400. During the spin coating process, the coating material mayspread and cover the whole top surface of the semiconductor substrate.In addition, the first baking process may be performed to thesemiconductor substrate 400, forming the first material layer 402 andthe second material layer 403 on the top surface of the semiconductorsubstrate 400 successively.

Further, the first material layer 402 may have a second flowability. Thesecond flowability may be smaller than the first flowability. The secondmaterial layer 403 may have a third flowability, and the thirdflowability may be larger than the second flowability, but equal or lessthan the first flowability. In addition, the first spin coating processand the first baking process may be performed together. That is, duringthe first spin coating process, a heat treatment may be performed to thesemiconductor substrate 400 at the same time. The heat treatment may beperformed by using certain heating device set underneath thesemiconductor substrate 400.

More specifically, during the first spin process, coating material mayspread on the top surface of the semiconductor substrate 400. At thesame time, the coating material on the top surface of the semiconductorsubstrate 400 may be cured, because solvent in the coating material maybe evaporated due to the heat treatment. As the heating time increases,portion of the coating material may be cured and may form the firstmaterial layer 402.

Further, if the duration of the first baking process is too short, orthe temperature is too low, the formed cured first material may be toothin. Thus, the second material layer 403 may contain too much coatingmaterial, and is bad for forming the uniformly-thicknessed thirdmaterial layer after performing a second spin coating processsubsequently. On the other hand, if the duration of the first bakingprocess is too long, or the temperature is too high, the formed curedfirst material may be too thick. Thus, the second material layer 403 maycontain too few coating material, and is also bad for forming theuniformly-thicknessed third material layer after performing the secondspin coating process subsequently.

Thus, the first baking process may be performed with a temperatureranging from 60° C. to 200° C., and a baking duration ranging from 1seconds to 300 seconds. The first spin coating process may be performedusing a spin speed ranging from 1000 rpm to 3000 rpm, and a spin coatingduration ranging from 30 seconds to 300 seconds.

As shown in FIG. 16, performing the second spin coating process byrotating the semiconductor substrate 400 with the second spin speed.During the second spin coating process, coating material in the secondmaterial layer 403 (FIG. 15) having the second flowability may flow onthe surface of the first material layer 402, and may form auniformly-thicknessed third material layer 404.

The detailed parameters for the second spin coating process are similarwith the second spin coating process used for forming the third materiallayer 205 (FIG. 5) illustrated in the previous embodiment, thus, areomitted here.

As shown in FIG. 17, after the second spin coating process, performingthe second baking process to the first material layer 402 (FIG. 16) andthe third material layer 404 (FIG. 16) to from a coating layer 405 onthe top surface of the semiconductor substrate 400.

The detailed parameters of the second baking process is similar with thesecond baking process illustrated in the previous embodiment, thus, areomitted here. During the second baking process, solvent in the firstmaterial layer 402 may be further evaporated, and solvent in the thirdmaterial layer 404 may be evaporated. Thus, the flowability of the firstmaterial layer 402 and the third material layer 404 may decrease. Thefirst material layer 402 and the third material layer 404 may be cured,and may form the coating layer 405 on the top surface of thesemiconductor substrate 400.

According to the above analysis, embodiments consistent with the presentdisclosure may include the following advantages:

First, after spraying the coating material to the top surface of thesemiconductor substrate, the first spin coating process is performed tomake the coating material cover the whole surface of the semiconductorsubstrate. Next, the first baking process is performed to bake thesemiconductor substrate. Thus, a stacked structure made of the firstmaterial layer and the second material layer may be formed. The firstmaterial layer may be cured and may have a uniform thickness. Coatingmaterial in the second material layer may be still flowable. Then, thesecond spin coating process may be performed to the semiconductorsubstrate. Because the first material layer is cured, the first materialmay not flow. During the second spin coating process, only coatingmaterial in the second material layer may flow on the surface of thefirst material layer. In addition, the second material layer may have areduced coating material quantity compared to the initial coating layer.Thus, the second material layer may be impacted less by the centrifugalforce (centrifugal force may be proportional to the material mass).Thereby, coating material in the second material layer aggregating morein the edge region and less in the central region may be avoided. Thatis, by driving the second material layer flow on the surface of thefirst material layer, the second material layer may be easilytransformed into the uniformly-thicknessed third material layer. Becausethe first material layer and the third material layer may all have auniform thickness, the coating layer formed after the second bakingprocess may have a uniform thickness. The formed coating layer may havean improved thickness uniformity, and the semiconductor manufacturingmay have an increased production yields.

Second, in the disclosed embodiments, to form a uniformly-thicknessedcoating layer, the coating material may be sprayed to the semiconductorsurface for only one time. Thus, large amount of coating material beingthrown out of the semiconductor substrate surface may be avoided. Theformed coating layer may consume only a minimum amount of coatingmaterial. And, the production cost may be reduced.

Third, by performing the first spin coating process and the first bakingprocess together, the time needed for forming the coating layer may bereduced. Thus, the production cycle may be shortened.

Fourth, in certain embodiments, after the first spin coating process butprior the second baking process, the first baking process may berepeated multiple times. In addition, after each first baking process,the second spin coating process may be performed. Thus, beforeperforming the second baking process, the third material layer having auniform thickness may be formed. Further, the disclosedphotolithographic method may be used for forming relative thick (e.g.,50 μm˜5000 μm) coating layers. After repeating the first baking and thesecond spin coating process multiple times, the formed coating layer mayhave an improved thickness uniformity.

Embodiments consistent with the current disclosure provide aphotolithographic method for forming a coating layer. Otherapplications, advantages, alternations, modifications, or equivalents tothe disclosed embodiments are obvious to those skilled in the art. It isintended that the specification and examples be considered as exemplaryonly, with a true scope and spirit of the invention being indicated bythe claims.

What is claimed is:
 1. A photolithographic method for forming a coatinglayer, comprising: spraying coating material having a first flowabilityto a top surface of a provided semiconductor substrate; performing afirst spin coating process by rotating the semiconductor substrate witha first spin speed to form an initial coating layer covering the topsurface of the semiconductor substrate; performing a first bakingprocess to the initial coating layer to form a first material layerhaving a second flowability and a second material layer having a thirdflowability, wherein the second flowability is less than the firstflowability and the third flowability is larger than the secondflowability but less than the first flowability; performing a secondspin coating process by rotating the semiconductor substrate with asecond spin speed to drive the coating material in the second materiallayer flowing on the surface of the first material layer to form a thirdmaterial layer with a uniform thickness; and performing a second bakingprocess to the first material layer and the third material layer to forma final coating layer on the top surface of the semiconductor substrate.2. The method according to claim 1, wherein: the first baking process isperformed to the semiconductor substrate after the first spin coatingprocess.
 3. The method according to claim 1, wherein: after performingthe first spin coating process but prior to performing the second bakingprocess, the first baking process is repeated one or more times to formthe third material layer with a uniform thickness; and after performingeach first baking process, the second spin coating process is performed.4. The method according to claim 3, wherein, after performing the firstspin coating process but prior performing the second baking process,repeating the first baking process further includes: performing thefirst baking process to the semiconductor substrate for a first time toform the second material layer and a fourth material layer successivelyon the top surface of the semiconductor substrate; performing the secondspin coating process to the semiconductor substrate for a first time totransform the fourth material layer into a fifth material layer,performing the first baking process to the semiconductor substrate for asecond time, wherein, the second material layer has an increasedthickness and is transformed into a six material layer, the fifthmaterial layer has a reduced thickness and is transformed into a seventhmaterial layer; performing the second spin coating process to thesemiconductor substrate for a second time to transform the seventhmaterial layer into an eighth material layer; performing the firstbaking process to the semiconductor substrate for a third time, wherein,the sixth material layer has an increased thickness and is transformedinto the first material layer, the eighth material layer has a reducedthickness and is transformed into a ninth material layer; and performingthe second spin coating process to the semiconductor substrate for athird time to transform the ninth material layer into theuniformly-thicknessed third material layer.
 5. The method according toclaim 4, wherein: a spin speed used in performing the second coatingprocess for the second time is larger than a spin speed used inperforming the second coating process for the first time, and a spinspeed used in performing the second coating process for the third timeis larger than the spin speed used in performing the second coatingprocess for the second time.
 6. The method according to claim 2,wherein: the first baking process is a fast baking process having abaking temperature ranging from approximately 60° C. to 200° C., and abaking duration ranging from approximately 1 second to 300 seconds. 7.The method according to claim 1, wherein: the first spin coating processand the first baking process are performed at the same time.
 8. Themethod according to claim 7, wherein: the first baking process uses atemperature ranging from approximately 60° C. to 200° C., and a bakingduration ranging from approximately 1 second to 300 seconds.
 9. Themethod according to claim 1, wherein: the second spin speed is fasterthan the first spin speed.
 10. The method according to claim 9, wherein:the first spin speed ranges from approximately 400 rpm to 1000 rpm, andthe second spin speed ranges from approximately 1000 rpm to 2000 rpm.11. The method according to claim 1, wherein: the coating material isphotoresist or polyimide.
 12. The method according to claim 1, wherein:the formed final coating layer has a thickness ranging fromapproximately 50 μm to 5000 μm.
 13. The method according to claim 1,wherein: the coating material is sprayed in the central region on thetop surface of the semiconductor substrate.
 14. The method according toclaim 1, wherein: the second baking process uses a temperature rangingfrom approximately 90° C. to 400° C., and a baking duration ranging fromapproximately 30 second to 1000 seconds.
 15. The method according toclaim 1, wherein: during the spin coating process, gas is blown on tothe backside of the semiconductor substrate to prevent the coatingmaterial flowing to the back surface of the semiconductor substrate. 16.A photolithographic method for forming a coating layer, comprising:spraying coating material having a first flowability to a top surface ofa provided semiconductor substrate; performing a first spin coatingprocess with a first spin speed and performing a first baking processsimultaneously to form a first material layer having a secondflowability and a second layer having a third flowability; performing asecond spin coating with a second spin speed to drive the coatingmaterial in the second material layer flowing on the surface of thefirst material layer to form a third material layer with a uniformthickness; and performing a second baking process to the first materiallayer and the third material layer to form a final coating layer on thetop surface of the semiconductor substrate.
 17. The method according toclaim 16, wherein performing the first baking process further includes:heating underneath the semiconductor substrate to bake the semiconductorsubstrate during the first spin coating process.
 18. The methodaccording to claim 16, wherein: the first spin coating process uses afirst spin speed ranging from approximately 1000 rpm to 3000 rpm, and aspin coating duration ranging from approximately 30 seconds to 3000seconds.
 19. The method according to claim 16, wherein: the first bakingprocess uses a baking temperature ranging from approximately 60° C. to200° C., and a baking duration ranging from approximately 1 seconds to300 seconds.